1. Field of the Invention
The present invention relates to a method for synchronizing frames by using pilot patterns in a compressed mode.
2. Background of the Related Art
Recent 3GPP(Third Generation Partnership Project) has description of a transport channel and physical channel for further developed next generation mobile communication. With regard to the physical channel, a DPCH (Dedicated Physical Channel) is used for an up link and a downlink. In general, the DPCH consists of hierarchal layers of super frames, radio frames, and time slots. There are two types of DPCH; one is a DPDCH (Dedicated Physical Data Channel) and the other one is a DPCCH (Dedicated Physical Control Channel). The DPDCH is for transportation of dedicated data, and the DPCCH is for transportation of control information. The DPCCH has a plurality fields, such as a pilot, a TFCI, an FBI, and a TPC. The pilot Npilot is provided with pilot bits (or symbols) for supporting channel estimation for making coherent detection, and pilot bits (or symbols) for frame synchronization. Particularly, it is very important to make, identify, and failure detection of frame synchronization by using pilot patterns of the pilot Npilot, at a receiver side of the next generation mobile communication system. The following table 1 shows frame synchronization words used in the up link and down link DPCH.
TABLE 1Frame Synchronization WordsC1 = (1 0 0 0 1 1 1 1 0 1 0 1 1 0 0)C2 = (1 0 1 0 0 1 1 0 1 1 1 0 0 0 0)C3 = (1 1 0 0 0 1 0 0 1 1 0 1 0 1 1)C4 = (0 0 1 0 1 0 0 0 0 1 1 1 0 1 1)C5 = (1 1 1 0 1 0 1 1 0 0 1 0 0 0 1)C6 = (1 1 0 1 1 1 0 0 0 0 1 0 1 0 0)C7 = (1 0 0 1 1 0 1 0 1 1 1 1 0 0 0)C8 = (0 0 0 0 1 1 1 0 1 1 0 0 1 0 1)
The codes in the table 1 have auto-correlation function as expressed in the following equation (1).                                           R            i                    ⁡                      (            τ            )                          =                  {                                                                                          15                    ,                                                                                        τ                    =                    0                                                                                                                                          -                      1                                        ,                                                                                        τ                    ≠                    0                                                                        ,                          i              =              1                        ,            2            ,            …            ⁢                                                   ,            8                                              (        1        )            
The Rim(τ) in the equation (1) is an auto-correlation function of a frame synchronization word Ci. The codes in the table 1 may be classed in four as expressed in the following equation (2).E={C1, C2}, F={C3, C4}, G={C5, C6}, H={C7, C8}  (2)
Each of code pairs in each class has a cross correlation function as expressed in the following equations (3) and (4).                                           R                          i              ,              j                                ⁡                      (            τ            )                          =                  {                                                                                          -                    15                                    ,                                                                              τ                  =                  7                                                                                                      1                  ,                                                                              τ                  ≠                  7                                                                                        (        3        )                                                      R                          j              ,              i                                ⁡                      (                          τ              +              1                        )                          =                  {                                                                                          -                    15                                    ,                                                                              τ                  =                  7                                                                                                      1                  ,                                                                              τ                  ≠                  7                                                                                        (        4        )            
Where i, j=1, 2, . . . , 8, and Ri,j(τ) represents a cross-correlation function between code pairs in each of the classes E, F, G, H. Eventually, a result of correlation as expressed in the following equation (5) can be obtained by appropriate combination of the frame synchronization words according to the auto-correlation function as expressed in the equation (1), and a correlation result as the following equation (6) can be obtained by appropriate combination of codes in each of the classes according to the cross-correlation function as expressed by the equations (3) and (4).                                           ∑                          i              =              1                        α                    ⁢                                    R              i                        ⁡                          (              τ              )                                      =                  {                                                                                                                α                      ·                      15                                        ,                                                                                        τ                    =                    0                                                                                                                                          -                      α                                        ,                                                                                        τ                    ≠                    0                                                                        ,                          α              =              1                        ,            2            ,            3            ,            …            ⁢                                                   ,            8                                              (        5        )                                                      ∑                          o              =              1                                      α              /              2                                ⁢                      (                                                            R                                                                                    2                        ⁢                        i                                            -                      1                                        ,                                          2                      ⁢                      i                                                                      ⁡                                  (                  τ                  )                                            +                                                R                                                            2                      ⁢                      i                                        ,                                                                  2                        ⁢                        i                                            -                      1                                                                      ⁡                                  (                                      τ                    +                    1                                    )                                                      )                          =                  {                                                                                                                                        -                        α                                            ·                      15                                        ,                                                                                        τ                    =                    0                                                                                                                    α                    ,                                                                                        τ                    ≠                    0                                                                        ,                          α              =              1                        ,            2            ,                          3.              ⁢              …                        ⁢                                                   ,            8                                              (        6        )            
FIG. 1A illustrates a graph showing an auto-correlation result when α=2 in the equation (5), and FIG. 1B illustrates a graph showing a cross-correlation result between codes in the same class when α=2 in the equation (6). FIG. 2A illustrates a graph showing an auto-correlation result when α=4 in the equation (5), and FIG. 2B illustrates a graph showing a cross-correlation result between a pair of codes of class ‘E’ and ‘F’ when α=4 in the equation (6). For an example, as can be known from FIG. 2A, the auto-correlation function of the frame synchronization words shown in table 1 has a maximum correlation result at a delay time point ‘0’ (τ=0), and a minimum correlation result at a sidelobe which is a delay time point other than the delay time point ‘0’. As can be known from FIG. 2B, the cross-correlation function of each code pair of the frame synchronization words in the same class shows a maximum correlation result of a negative polarity at a middle delay point τ=7.
Thus, in the related art, the frame synchronization is attained, and identified by using correlation of the frame synchronization words shown in table 1. However, though a performance of attaining the frame synchronization can be made properly when 15 slots are transported for one frame, the performance can not be made properly when a minimum 8 slots and maximum 14 slots are transported for one frame like in a compressed mode which is a character of a W-CDMA. Moreover, in the related art, correlation of pilot patterns are made for identification of frame synchronization and detection of the out-of frame synchronization. When identification of the frame synchronization and detection of the out-of frame synchronization is made from a result of pilot pattern correlation, a preset threshold value is provided in the related art for comparing the correlation value calculated for each slot and the threshold value, to identify the synchronization and detect an out-of synchronization.
However, it is evident that the threshold values in the related art set freely as the mobile station UE or the base station Node B likes causes failure in the frame synchronization identification or out-of frame synchronization detection owing to different threshold values, that may be one of great problem in global roaming the next generation mobile communication system pursues. Accordingly, a universal reference for determining the frame synchronization identification and the out-of frame synchronization detection is required, and a method for making positive frame synchronization identification and detection of out-of frame synchronization is required.